Option to ignore concurrent changes to files read

[koertkuipers]

Description

Resolves https://github.com/delta-io/delta/issues/1304

How was this patch tested?

Added tests to DeltaSinkSuite, DeltaSuite and OptimisticTransactionSuite

Does this PR introduce any user-facing changes?

Yes, user can now set .option("ignoreReadChanges", "true") on writes